Schedule II - Condensed Financial Information of Registrant (Details) (USD $)	3 Months Ended										12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
ASSETS
Short-term investments	$ 56,165,534					$ 53,418,914					$ 56,165,534		$ 53,418,914
Cash	238,821					330,392					238,821		330,392		255,042
Accounts receivable	1,079,693					2,390,955					1,079,693		2,390,955
Income taxes recoverable	0					1,588,089					0		1,588,089
Total assets	1,821,397,652					1,687,063,626					1,821,397,652		1,687,063,626
LIABILITIES
Amounts due affiliate to settle inter-company transaction balances	13,521,861					19,127,010					13,521,861		19,127,010
Total liabilities	923,722,685					889,499,942					923,722,685		889,499,942
STOCKHOLDERS' EQUITY
Common stock, $1 par value, authorized 20,000,000 shares; issued and outstanding, 13,306,027 shares in 2013 and 12,909,457 shares in 2012	13,306,027					12,909,457					13,306,027		12,909,457
Additional paid-in capital	99,308,749					89,205,881					99,308,749		89,205,881
Accumulated other comprehensive income	59,010,489	[1]				47,752,375	[1]				59,010,489	[1]	47,752,375	[1]
Retained earnings	283,584,971					251,341,451					283,584,971		251,341,451
Total stockholders' equity	455,210,236					401,209,164					455,210,236		401,209,164		352,340,595	362,852,917
Total liabilities and stockholders' equity	1,378,932,921					1,290,709,106					1,378,932,921		1,290,709,106
REVENUES
Investment loss											43,022,175		44,145,074		46,110,925
Total revenues	146,686,003		144,109,477	138,566,944	133,842,713	128,727,934		132,562,158	120,503,570	130,073,865	568,351,347		511,867,527		472,644,641
Other expenses											2,481,306		2,122,254		2,672,654
Income Tax Expense (Benefit)	6,995,658		2,365,223	1,736,419	6,236,447	5,498,854		2,429,112	(2,935,333)	8,674,552	17,333,747		13,667,185		(8,254,238)
Net income (loss)	15,834,277		7,199,643	6,212,236	14,272,517	12,997,921		8,321,244	(2,576,471)	19,223,735	43,518,673		37,966,429		(2,737,279)
Condensed Statements of Comprehensive Income [Abstract]
Net income (loss)	15,834,277		7,199,643	6,212,236	14,272,517	12,997,921		8,321,244	(2,576,471)	19,223,735	43,518,673		37,966,429		(2,737,279)
OTHER COMPREHENSIVE INCOME (LOSS)
Change in unrealized holding gains (losses) on investment securities, net of deferred income taxes											(15,581,644)		23,862,752		19,894,900
Reclassification adjustment for realized investment gains included in net income (loss), net of income taxes											(5,847,754)		(5,211,069)		(6,103,052)
Change in unrealized holding gains on fixed maturity securities with other-than-temporary impairment, net of deferred income taxes											0		0		13,941
Reclassification adjustment for realized investment losses from fixed maturity securities with other-than-temporary impairment included in net income (loss), net of income taxes											0		0		(55,911)
Reclassification adjustment for amounts amortized into net periodic pension and postretirement benefit cost, net of deferred income taxes:
Net actuarial loss											1,881,540		2,108,504		1,034,037
Prior service credit											(460,319)		(344,247)		(316,050)
Total reclassification adjustment associated with affiliate's pension and postretirement benefit plans											1,421,221		1,764,257		717,987
Change in funded status of affiliate's pension and postretirement benefit plans, net of deferred income taxes:
Net actuarial gain (loss)											13,718,056		(735,887)		(11,768,434)
Prior service credit											17,548,235		731,812		33,770
Total change in funded status of affiliate's pension and postretirement benefit plans											31,266,291		(4,075)		(11,734,664)
Other comprehensive income											11,258,114	[1]	20,411,865		2,845,023
Total comprehensive income											54,776,787		58,378,294		107,744
Condensed Statements of Cash Flows [Abstract]
Net cash provided by operating activities											86,832,946		55,038,140		11,765,491
Cash flows from investing activities
Net (purchases) sales of short-term investments											(2,786,194)		(10,789,988)		(6,012,815)
Net cash (used in) provided by investing activities											(85,952,893)		(45,213,281)		(1,192,345)
Cash flows from financing activities
Issuance of common stock through affiliate’s stock plans											10,208,452		691,552		974,493
Excess tax benefit associated with affiliate’s stock plans											95,077		(2,221)		6,622
Repurchase of common stock											0		0		(1,849,896)
Dividends paid to stockholders (affiliated ($6,749,153), ($6,356,760) and ($6,042,846))											(11,275,153)		(10,438,840)		(9,941,317)
Net cash used in financing activities											(971,624)		(9,749,509)		(10,810,098)
Net increase (decrease) in cash											(91,571)		75,350		(236,952)
Cash at the beginning of the year					330,392					255,042	330,392		255,042		491,994
Cash at the end of the year	238,821					330,392					238,821		330,392		255,042
Income taxes recovered											13,713,541		3,514,432		(1,759,507)
Interest paid											900,000		900,000		900,000
Parent company [Member]
ASSETS
Investment in common stock of subsidiaries (equity method)	441,983,975					396,288,097					441,983,975		396,288,097
Short-term investments	12,686,803					3,972,400					12,686,803		3,972,400
Cash	149,544					291,417					149,544		291,417		122,459
Prepaid assets	66,665					75,831					66,665		75,831
Accounts receivable	0					167,165					0		167,165
Income taxes recoverable	480,756					458,197					480,756		458,197
Amounts due from affiliate to settle inter-company transaction balances	0					66,423					0		66,423
Total assets	455,367,743					401,319,530					455,367,743		401,319,530
LIABILITIES
Accounts payable	100,771					110,366					100,771		110,366
Amounts due affiliate to settle inter-company transaction balances	56,736					0					56,736		0
Total liabilities	157,507					110,366					157,507		110,366
STOCKHOLDERS' EQUITY
Common stock, $1 par value, authorized 20,000,000 shares; issued and outstanding, 13,306,027 shares in 2013 and 12,909,457 shares in 2012	13,306,027					12,909,457					13,306,027		12,909,457
Additional paid-in capital	99,308,749					89,205,881					99,308,749		89,205,881
Accumulated other comprehensive income	59,010,489					47,752,375					59,010,489		47,752,375
Retained earnings	283,584,971					251,341,451					283,584,971		251,341,451
Total stockholders' equity	455,210,236					401,209,164					455,210,236		401,209,164
Total liabilities and stockholders' equity	455,367,743					401,319,530					455,367,743		401,319,530
REVENUES
Dividends received from subsidiaries											9,973,741		12,050,096		10,000,064
Investment loss											(9,473)		(9,754)		(2,861)
Total revenues											9,964,268		12,040,342		9,997,203
Other expenses											1,364,115		1,299,379		1,330,129
Income before income tax benefit and equity in undistributed net income (loss) of subsidiaries											8,600,153		10,740,963		8,667,074
Income Tax Expense (Benefit)											(480,756)		(462,178)		(466,548)
Income before equity in undistributed net income (loss) of subsidiaries											9,080,909		11,203,141		9,133,622
Equity in undistributed net income (loss) of subsidiaries											34,437,764		26,763,288		(11,870,901)
Net income (loss)											43,518,673		37,966,429		(2,737,279)
Condensed Statements of Comprehensive Income [Abstract]
Net income (loss)											43,518,673		37,966,429		(2,737,279)
OTHER COMPREHENSIVE INCOME (LOSS)
Change in unrealized holding gains (losses) on investment securities, net of deferred income taxes											(15,581,644)		23,862,752		19,894,900
Reclassification adjustment for realized investment gains included in net income (loss), net of income taxes											(5,847,754)		(5,211,069)		(6,103,052)
Change in unrealized holding gains on fixed maturity securities with other-than-temporary impairment, net of deferred income taxes											0		0		13,941
Reclassification adjustment for realized investment losses from fixed maturity securities with other-than-temporary impairment included in net income (loss), net of income taxes											0		0		55,911
Reclassification adjustment for amounts amortized into net periodic pension and postretirement benefit cost, net of deferred income taxes:
Net actuarial loss											1,881,540		2,108,504		1,034,037
Prior service credit											(460,319)		(344,247)		(316,050)
Total reclassification adjustment associated with affiliate's pension and postretirement benefit plans											1,421,221		1,764,257		717,987
Change in funded status of affiliate's pension and postretirement benefit plans, net of deferred income taxes:
Net actuarial gain (loss)											13,718,056		(735,887)		(11,768,434)
Prior service credit											17,548,235		731,812		33,770
Total change in funded status of affiliate's pension and postretirement benefit plans											31,266,291		(4,075)		(11,734,664)
Other comprehensive income											11,258,114	[1]	20,411,865		2,845,023
Total comprehensive income											54,776,787		58,378,294		107,744
Condensed Statements of Cash Flows [Abstract]
Net cash provided by operating activities											9,544,154		11,116,544		9,069,618
Cash flows from investing activities
Net (purchases) sales of short-term investments											(8,714,403)		(1,198,077)		1,481,321
Net cash (used in) provided by investing activities											(8,714,403)		(1,198,077)		1,481,321
Cash flows from financing activities
Issuance of common stock through affiliate’s stock plans											10,208,452		691,552		974,493
Excess tax benefit associated with affiliate’s stock plans											95,077		(2,221)		6,622
Repurchase of common stock											0		0		(1,849,896)
Dividends paid to stockholders (affiliated ($6,749,153), ($6,356,760) and ($6,042,846))											(11,275,153)		(10,438,840)		(9,941,317)
Net cash used in financing activities											(971,624)		(9,749,509)		(10,810,098)
Net increase (decrease) in cash											(141,873)		168,958		(259,159)
Cash at the beginning of the year					291,417					122,459	291,417		122,459		381,618
Cash at the end of the year	149,544					291,417					149,544		291,417		122,459
Income taxes recovered											0		470,528		467,140
Interest paid											$ 0		$ 0		$ 0

[1] All amounts are net of tax. Amounts in parentheses indicate debits.